<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="../vue.js"></script>
</head>
<body>
    <h1>hello world </h1>
    <div id = "box">
        {{10 + 19}}
        {{username}}
    </div>
    <script>
        Vue.createApp({
            data(){
                return {
                    username:"lhy"
                }
            }
        }).mount("#box")
    </script>
</body>
</html>